Process for coating metal surfaces

ABSTRACT

A process for coating metal surfaces in which an uncured resin coating is formed on the surface of a metal by contacting the metal surface with an autodepositing coating composition that contains acid, oxidizing agent, and water-dispersible or water-soluble organic film-forming resin, and the uncured coating is thereafter dried, produces a strongly adherent, highly corrosion-resistant autodeposited coating when the uncured coating is brought, prior to its drying, into contact with an aqueous solution that has a pH adjusted to 7 to 11 and that contains at least one selection from the following inorganic acids and salts thereof: molybdic acid, tungstic acid, polyphosphoric acid, and polysilicic acid.

TECHNICAL FIELD

The invention relates to a process for coating metal surfaces. Morespecifically, the invention relates to a process that produces highlycorrosion-resistant and strongly adherent resin coatings on metalsurfaces. This process is applied to the uncured resin coatings that areformed on metal surfaces when the surface of a metal is brought intocontact with an autodepositing coating composition that contains acid,oxidizing agent, and water-dispersible or water-soluble organicfilm-forming resin. The process consists of contacting an uncured resincoating of this type with an aqueous solution that has a pH adjusted to7 to 11 and that contains at least 1 selection from the followinginorganic acids and salts thereof: molybdic acid, tungstic acid,polyphosphoric acid, and polysilicic acid.

BACKGROUND ART

Autodepositing coating compositions as referred to in this invention areacidic coating compositions that contain an organic film-forming resinand that produce a resin coating on the surface of metal brought intocontact with the composition. Compositions of this type are disclosed inJapanese Patent Publication Numbers Sho 47-17630 17,630/1972!, Sho48-14412 14,412/1973!, Sho 52-21006 21,006/1977!, Sho 52-3569235,692/1977!, Sho 53-15093 15,093/1978!, Sho 53-16010 16,010/1978!, Sho53-44949 44,949/1978!, and Sho 54-13435 13,435/1979! and in JapanesePatent Application Laid Open Kokai or Unexamined! Numbers Sho 60-5847458,474/1985!, Sho 61-168673 168,673/1986!, and Sho 61-246267246,267/1986!.

A characteristic feature of these known coating compositions is thatimmersion of a clean metal surface in the coating composition produces aresin coating whose thickness or weight increases with increasingimmersion time. In addition, part of the metal ion eluted from the metalsurface by the chemical etching of the coating composition is taken intothe coating; this makes possible the efficient formation of a resincoating on the metal surface without utilizing externally suppliedelectricity as is used in the electrodeposition of coatings.

The conventional coating compositions, however, do not themselves alwaysexhibit a satisfactory adherence or corrosion resistance, and as aresult various treatment processes have been examined for the purpose ofimproving the adherence and corrosion resistance of autodepositedcoatings on metal surfaces. For example, Japanese Patent ApplicationLaid Open Number Sho 52-56142 56,142/1977! teaches the use of a rinse inautodepositing coating processes that consist of application of awaterborne coating composition to a metal substrate followed by baking.This rinse is applied to the uncured autodeposited film between thedeposition step and baking step and consists of an aqueous solution orwaterborne dispersion whose main component is at least one selectionfrom the group comprising the silicofluorides, borofluorides,titanofluorides, aluminofluorides, and nitrites. The application of thisprocess makes possible the production, without the use ofrust-preventing pigments, of autodeposited films that have a goodcorrosion resistance.

Japanese Patent Application Laid Open Number Sho 52-68240 68,240/1977!teaches a rinse that, as in Japanese Patent Application Laid Open NumberSho 52-56142, is applied to the uncured autodeposited coating betweenthe deposition step and the baking step. In this case, however, therinse consists of an aqueous solution or waterborne dispersion whosemain component is at least one selection from the group comprisingamines, the amine salts of carboxylic acids, amino salts, melamine, andamides. The practice of this process is again reported to make possiblethe production of good corrosion-resistant autodeposited films withoutthe use of rust-preventing pigments. Japanese Patent Application LaidOpen Number Sho 60-58474 teaches a process that improves the waterresistance of the coatings. In this process, an aqueous alkali metal orammonium hydroxide solution is applied to the uncured autodeposited filmon the metal surface prior to drying. This makes the dried filmimpermeable to water and thereby improves the water resistance.

U.S. Pat. Nos. 3,647,567 and 4,030,945 and Japanese Patent ApplicationLaid Open Number Sho 61-168673 teach the preparation of goodcorrosion-resistant autodeposited films by a pre-drying rinse of theuncured autodeposited film on the metal surface with a chromiumcompound-containing aqueous solution.

In recent years, higher added value has been sought from the painting ofmetal surfaces, and in particular a higher corrosion resistance andhigher adherence are desired. The art described hereinbefore, however,is not at a level that can consistently satisfy the requiredperformance.

DISCLOSURE OF THE INVENTION Problems to Be Solved by the Invention

The invention takes as its object the introduction of a process forcoating metal surfaces that is able to coat metal surfaces with anautodeposited coating that has an adherence and corrosion resistancesuperior to those of the autodeposited coatings afforded by the priorart.

SUMMARY OF THE INVENTION

An autodeposited coating with an adherence and corrosion resistance farsuperior to the corresponding values provided by the prior art can beproduced by the application before drying of a specific type of aqueoussolution to the uncured resin coating formed on metal surfaces bycontact with an autodepositing coating composition.

In specific terms, in the metal surface coating process in which anuncured resin coating is formed on the surface of a metal by contactingthe metal surface with an autodepositing coating composition thatcontains acid, oxidizing agent, and water-dispersible or water-solubleorganic film-forming resin, and the uncured coating is thereafter dried,the invention provides a process which is characterized in that saiduncured coating is brought, prior to its drying, into contact with anaqueous solution that has a pH adjusted to 7 to 11 and that contains atleast one selection from the following inorganic acids and saltsthereof: molybdic acid, tungstic acid, polyphosphoric acid, andpolysilicic acid.

Suitable metal substrates for the invention are specifically exemplifiedby ferriferous metals, zinciferous metals, aluminiferous metals, and thelike.

The known autodepositing coating compositions are highly suitable foruse as the autodepositing coating composition employed in the presentinvention. Some examples thereof are the coating compositions disclosedin Japanese Patent Publication Number Sho 54-13453 13,453/1979!, one ofwhich consists of approximately 5 to 550 g/L as solids of a dispersedresin, approximately 0.4 to 5.0 g/L of hydrofluoric acid as acidcomponent, approximately 0.3 to 3.0 g/L of hydrogen peroxide asoxidizing agent, and, optionally, water-dispersible pigment. Otherexamples are the coating compositions disclosed in Japanese PatentPublication Number Sho 52-35692, one of which consists of approximately5 to 550 g/L as solids of a dispersed resin, approximately 0.4 to 5.0g/L of hydrofluoric acid as acid component, no more than approximately3.0 g/L of hydrogen peroxide as oxidizing agent, approximately 1 to 50g/L of ferric fluoride as a metal compound component and co-oxidizingagent, and, optionally, water-dispersible pigment.

The inorganic acids used by the present invention are molybdic acid,tungstic acid, polyphosphoric acid, and polysilicic acid. The saltsusable by the invention include the sodium salts, ammonium salts,calcium salts, potassium salts, and the like. The invention uses atleast one selection from these inorganic acids and salts thereof.

DESCRIPTION OF PREFERRED EMBODIMENTS

The preferred content of the total of the inorganic acid(s)characteristic of the invention and salt(s) thereof in an aqueoussolution used for treatment according to the invention preferably is,with increasing preference in the order given, at least 0.01, 0.05,0.10, 0.30, 0.50, 0.70, 0.80, 0.90, or 1.0 grams per liter (hereinafterusually abbreviated as "g/L") and independently preferably is, withincreasing preference in the order given, not more than 50, 40, 30, 20,15, 13, 11, 9.0, 8.5, 8.0, 7.5, 7.0, 6.8, or 6.6 g/L. The effect fromaddition is usually insignificant at concentrations below 0.01 g/L,while additions in excess of 50 g/L are undesirable from a qualitystandpoint because such additions degrade the appearance of the coatingand also its adherence and corrosion resistance.

The pH of the aqueous solution used by the invention is preferablyadjusted before use into and maintained during use at a value that is,with increasing preference in the order given, not less than 7.00, 7.05,7.10, 7.15, or 7.18 and independently preferably is, with increasingpreference in the order given, not more than 11, 10.7, 10.4, 10.2, 10.1,10.0, 9.9, or 9.8. An improved adherence and corrosion resistance cannot normally be expected when the pH is substantially outside thisrange. Alkaline materials, for example, can be used to adjust the pHinto this preferred range. While no narrow restrictions apply toalkaline materials usable in the present invention, ammonium bicarbonateand ammonium hydroxide are preferred. In addition to bases, inorganicacids, organic acids, and their salts may also be used to adjust the pHof the aqueous solution; for example, hydrofluoric acid, nitric acid,sulfuric acid, phosphonic acid, phosphinic acid, citric acid, oxalicacid, tartaric acid, and the like may be used for pH adjustment. Theaqueous solution may contain an oxidizing agent, such as hydrogenperoxide and the like, as an optional component.

The wet uncured coatings are preferably rinsed with plain water beforebeing treated according to the invention, but should not be allowed todry before being contacted with the characteristic aqueous treatmentsolutions of this invention. After such contact with the aqueoustreatment solutions according to this invention, the coating preferablyis not rinsed before being dried.

The method for applying the aqueous solution to the uncuredautodeposited coating is not critical to the invention, but immersion ispreferred. The application temperature of the aqueous solution is alsonot critical, although for convenience, a normal ambient human comforttemperature of 20°±5° C. The contact time preferably is, with increasingpreference in the order given, at least 0.08, 0.16, 0.30, 0.50, 0.60,0.70, 0.80, 0.90, or 0.95 minutes (hereinafter usually abbreviated"min") and independently preferably is, with increasing preference inthe order given, not more than 10, 7, 5, 4, 3, 2, 1.8, 1.6, 1.4, 1.2, or1.1 min. Drying conditions also are not critical to the invention, butpreferably the maximum temperature during drying is, with increasingpreference in the order given, at least 30°, 50°, 70°, 90°, 100°, or105° C. and independently preferably is, with increasing preference inthe order given, not more than 250°, 230°, 220°, 210°, 200°, 190°, 185°,or 181° C. for acrylate type organic resins and not more than 120°,115°, 114°, 113°, 112°, 111°, or 110° C. for poly{vinylidene chloride}resins. Independently, the time at these temperatures preferably is,with increasing preference in the order given, at least 0.5, 1.0, 2.0,4.0, 7.0, 10, 12, 14, 16, 18, or 19 min and independently preferably is,with increasing preference in the order given, not more than 60, 50, 40,30, 28, 26, 24, 22, or 21 min.

The crux of the invention is that application of the subject aqueoussolution to the uncured autodeposited coating is able to produce astrongly adherent, highly corrosion-resistant autodeposited coating,possibly due to the formation of a passivation coating on the metalsurface. Such a passivation coating could be produced through theformation of complexes between anion supplied from the molybdic acid,tungstic acid, polyphosphoric acid, and/or polysilicic acid and/or saltsthereof present in the aqueous solution and metal cations taken up bythe autodeposited coating and particularly metal cations present on themetal surface by virtue of the uncured autodeposited film. Corrosion mayalso be inhibited through the formation of complexes between said anionsthat have been taken up by the coating and the metal cations elutingduring metal corrosion.

The invention is illustrated in greater detail below through working andcomparative examples. The test methods used to evaluate performance arealso explained below.

EXAMPLES Evaluation of coating adherence by the crosscut/tape peel test

A crosshatch pattern of one hundred 1 millimeter ("mm")×1 mm squares wascut in the test panel and peeled with adhesive tape, and the number ofremaining coating film squares was counted. This test was conducted bothbefore and after immersion in water at 40° C. for 240 hours.

Evaluation of coating adherence by the Du Pont impact test

A 1 kg impacter with a diameter of 1.27 centimeters ("cm") was droppedon the test panel and the impact zone was peeled with adhesive tape. Thevalue measured was the highest impacter drop-height in cm at which filmpeeling did not occur. This test was conducted both before and afterimmersion in water at 40° C. for 240 hours.

Evaluation of coating adherence by the Erichsen test

The test surface of the test panel was extruded 5 mm using an Erichsentest instrument, and the cupped region was then peeled with adhesivetape. Film peeling was evaluated according to the scale given below:

+++: no film peeling

++: area of film peeling is less than 2%

+: area of film peeling is less than 10%

x: area of film peeling is at least 10%.

This test was conducted both before and after immersion in water at 40°C. for 240 hours.

Corrosion resistance test

A cross was scribed in the coating on the test panel to reach the basemetal. The test panel was then subjected to salt spray testing (500hours for cold-rolled steel, galvannealed hot-dip zinc-coated steel, andelectrogalvanized steel; 1,000 hours for aluminum), and tape peeling wasconducted after this exposure. The evaluation consisted of measurementof the peel width (one side, in mm) from the cross scribe line.

Examples 1 to 6

Preliminarily cleaned panels (70×150×1 mm) of cold-rolled steel,galvannealed hot-dip zinc-plated steel, electrogalvanized steel, andaluminum were immersed for 180 seconds in autodepositing coatingcomposition A:

    ______________________________________                                        Component                Concentration                                        ______________________________________                                        Rhoplex ™ WL-91 acrylic resin latex, 41.5% solids                                                   120.50 g/L                                           (supplied by the Rohm and Haas Company)                                       Hydrofluoric acid        0.50 g/L                                             Hydrogen peroxide        0.05 g/L                                             Ferric fluoride          3.00 g/L                                             Deionized water          balance.                                             ______________________________________                                    

This composition was maintained at a bath temperature of approximately20° C. to 22° C. After a water rinse, the panels were immersed atambient temperature for 60 seconds in aqueous treating solution A, B, C,D, or E, with compositions shown in Table 1 below. This was followed byoven drying for 20 minutes at 180° C. and then testing. The results ofperformance testing on the test panels are reported in Table 2.

                                      TABLE 1                                     __________________________________________________________________________    Characteristic of the Aqueous                                                              Value of the Characteristic for Aqueous Treating Solution                     Composition Designated:                                          Treating Solutions                                                                         A  B  C  D  E  F  G  H  I  J  K  L                               __________________________________________________________________________    Molybdic acid, g/L                                                                         5.00                                                                             5.00                                                          Calcium molybdate, g/L                                                                        1.50                                                          Ammonium Molybdate, g/L                                                                             5.00        0.80                                                                             5.00                                     Tungstic acid, g/L 0.15                                                       Sodium tungstate, g/L                                                                            5.00     1.00                                              Polyphosphoric acid, g/L 0.25                                                 Sodium polyphosphate, g/L                                                                              3.50                                                 Sodium polysilicate, g/L       3.00                                           Ammonium Hydroxide, g/L                                                                    5.00                                                                             4.50                                                                             4.50  6.50                                                                             5.50                                                                             5.50                                                                             6.50                                                                             2.00  5.00                                                                             5.00                            Ammonium Bicarbonate, g/L                                                                           3.00              3.00                                  Nitric acid, g/L                     5.00                                     Phosphinic acid, g/L        0.20                                              Sodium phosphonate, g/L  0.65                                                 Citric acid, g,/L     0.80                                                    Ammonium Oxalate, g/L             0.50                                        Hydrogen peroxide, g/L                                                                     0.01                 0.01                                        pH           8.5                                                                              9.8                                                                              8.5                                                                              7.2                                                                              7.5                                                                              8.0                                                                              8.5                                                                              9.0                                                                              6.0                                                                              7.5                                                                              10.5                                                                             12.0                            __________________________________________________________________________

                                      TABLE 2                                     __________________________________________________________________________                                 Adherence Test Results:                                                                         Corro-                                                 Coating                                                                            Crosscut/                                                                           DuPont                                                                              Erichsen                                                                            sion                                      Type of Panel Coated:                                                                      Add-On,                                                                            Peel  Impact                                                                              Test  Re-                            AC:     ATC:                                                                             CRS                                                                              GHD                                                                              EG                                                                              Aluminum                                                                           gm.sup.2                                                                           Pre-I                                                                            Post-I                                                                           Pre-I                                                                            Post-I                                                                           Pre-I                                                                            Post-I                                                                           sistance                       __________________________________________________________________________    Example                                                                       Number                                                                        1    A  A  .check mark. 22   100                                                                              100                                                                              40 30 +++                                                                              +++                                                                              1.0                            2    A  B  .check mark. 24   100                                                                              100                                                                              40 40 +++                                                                              +++                                                                              1.0                            3    A  C  .check mark. 23   100                                                                              100                                                                              40 40 +++                                                                              ++ 1.5                            4    A  D  .check mark. 22   100                                                                              100                                                                              40 30 +++                                                                              +++                                                                              1.0                            5    A  E     .check mark.                                                                            21   100                                                                              100                                                                              40 40 +++                                                                              ++ 1.5                            6    A  E          .check mark.                                                                       20   100                                                                              100                                                                              50 40 +++                                                                              +++                                                                              0.5                            7    B  F  .check mark. 18   100                                                                              100                                                                              50 40 +++                                                                              +++                                                                              1.5                            8    B  G     .check mark.                                                                            17   100                                                                              100                                                                              40 40 +++                                                                              +++                                                                              1.0                            9    B  G        .check mark.                                                                         20   100                                                                              100                                                                              30 30 +++                                                                              ++ 1.5                            10   B  H  .check mark. 18   100                                                                              100                                                                              40 30 +++                                                                              ++ 1.5                            11   B  H          .check mark.                                                                       19   100                                                                              100                                                                              50 40 +++                                                                              +++                                                                              0.5                            Com-                                                                          parative                                                                      Example                                                                       Number                                                                        1    A  I  .check mark. 22   100                                                                              100                                                                              30 20 +  x  4.0                            2    A  J     .check mark.                                                                            24   100                                                                              100                                                                              20 20 +  x  3.5                            3    A  K        .check mark.                                                                         23   100                                                                              100                                                                              30 20 +  x  3.5                            4    A  L  .check mark. 24   100                                                                               95                                                                              20 20 +  x  4.5                            5    A  M  .check mark. 20   100                                                                              100                                                                              30 20 +  x  3.0                            6    B  J     .check mark.                                                                            17   100                                                                              100                                                                              30 20 +  +  3.5                            7    B  K          .check mark.                                                                       18   100                                                                              100                                                                              40 30 ++ +  2.5                            8    B  L  .check mark. 20   100                                                                               95                                                                              30 20 +  x  5.5                            __________________________________________________________________________     Notes for Table 2                                                             "AC" means "Autodepositing Composition"; "ATC" means "Aqueous Treatment       Composition"; "CRS" means "ColdRolled Steel"; "GHD" means "Galvannealed       HotDipped  ZincCoated Steel!"; "EG" means "Electrogalvanized  Steel!;         "PreI" means "PreImmersion"; "PostI" means "PostImmersion".              

Examples 7 to 11

Preliminarily cleaned panels (70×150×1 mm) of cold-rolled steel,galvannealed hot-dip zinc-coated steel, electrogalvanized steel, andaluminum were immersed for 180 seconds in autodepositing coatingcomposition B:

Autodepositing coating composition B

    ______________________________________                                        Component                 Concentration                                       ______________________________________                                        Daran ™ SL-143 vinylidene chloride copolymer resin la-                                               90.90 g/L                                           tex, 41.5% solids (supplied by W. R. Grace & Company)                         Hydrofluoric acid         0.50 g/L                                            Hydrogen peroxide         0.05 g/L                                            Ferric fluoride           3.00 g/L                                            Deionized water           balance.                                            ______________________________________                                    

This composition was maintained at a bath temperature of approximately20° C. to 22° C. After a water rinse, the panels were immersed for 60seconds in aqueous treating solution F, G, or H with compositionsreported in Table 1 at ambient temperature. This was followed by ovendrying for 20 minutes at 110° C. and then testing. The results ofperformance testing on the test panels are reported in Table 2.

Comparative Examples 1 to 4

Preliminarily cleaned panels (70×150×1 mm) of cold-rolled steel,galvannealed hot-dip zinc-coated steel, and electrogalvanized steel wereimmersed for 180 seconds in Autodepositing Coating Composition A asdescribed for Examples 1 to 6. The composition was maintained at a bathtemperature of approximately 20° to 22° C. After a water rinse, thepanels were immersed for 60 seconds in an aqueous solution I, J, K, or Lwith compositions as shown in Table 1 at ambient temperature. This wasfollowed by oven drying for 20 minutes at 180° C. and then testing. Theresults of performance testing on the test panels are reported in Table2.

Comparative Example 5

Preliminarily cleaned panels (70×150×1 mm) of cold-rolled steel wereimmersed for 180 seconds in the autodepositing coating composition Adescribed for Examples 1 to 6. The composition was maintained at a bathtemperature of approximately 20° C. to 22° C. After a water rinse, thepanels were immersed for 60 seconds at ambient temperature inchromium-containing aqueous solution containing 30 g/L of Palene® 60concentrate, supplied by Nihon Parkerizing Company, Ltd. This wasfollowed by oven drying for 20 minutes at 180° C. and then testing. Theresults of performance testing on the test panels are reported in Table2.

Comparative Examples 6 to 8

Preliminarily cleaned panels (70×150×1 mm) of cold-rolled steel,galvannealed hot-dip zinc-plated steel, and aluminum were immersed for180 seconds in the autodepositing coating composition B described forExamples 7 to 11. The composition was maintained at a bath temperatureof approximately 20° to 22° C. After a water rinse, the panels wereimmersed for 60 seconds in aqueous solution J, K, or L, withcompositions as reported in Table 1 at ambient temperature. This wasfollowed by oven drying for 20 minutes at 110° C. and then testing. Theresults of performance testing on the test panels are reported in Table2.

The conclusions set forth below can be drawn on the basis of Examples 1to 11 and Comparative Examples 1 to 8.

1. In Examples 1 to 11, both autodepositing coating compositions A and Bgave very good results for corrosion resistance and for film adherenceas evaluated by the crosscut/tape peel test, Du Pont impact test, andErichsen test.

2. In contrast to this, Comparative Examples 1,2, 3, and 4 gave poorerresults for film adherence (as evaluated by the Du Pont impact test andErichsen test) and corrosion resistance than were obtained in Examples 1to 11. The pH 6.0 used in Comparative Example 1 was too low, while thepH 12.0 used in Comparative Example 4 was too high. Comparative Examples2 and 3 used only base without the addition of an inorganic acid or saltthereof as specified for the invention. Comparative Example 4 also gavepoorer results in the crosscut/tape peel test.

3. Comparative Example 5 used a chromium compound-containing aqueoussolution from the prior art. While the film adherence as measured by theDu Pont impact test was only slightly poorer in Comparative Example 5than in Examples 1 to 11, the film adherence as measured by the Erichsentest and the corrosion resistance were substantially poorer.

4. Comparative Examples 6 and 8 used autodepositing coating compositionB in place of autodepositing coating composition A, but otherwisecorresponded to Comparative Examples 2 and 4, respectively. The trendsobserved for Comparative Examples 6 and 8 were the same as forComparative Examples 2 and 4, and the former thus exhibited a filmadherence and corrosion resistance inferior to Examples 1 to 11.

5. Comparative Example 7 corresponded to Comparative Example 3, exceptthat the former used autodepositing coating composition B in place ofautodepositing coating composition A and used an aluminum panel as thecoated panel in place of an electrogalvanized steel panel. Nevertheless,Comparative Example 7 still had a film adherence as measured by the DuPont impact and Erichsen tests and a corrosion resistance inferior tothose of Example 11.

BENEFITS OF THE INVENTION

The process for coating metal surfaces in accordance with the presentinvention forms an autodeposited coating whose adherence and corrosionresistance are superior to those of coatings produced by the heretoforeknown processes.

The invention claimed is:
 1. A process for coating a metal surface, saidprocess comprising steps of(A) contacting the metal surface with anautodepositing coating composition that comprises acid, oxidizing agent,and water-dispersible or water-soluble organic film-forming resin for asufficient time to form on the metal surface a wet uncured coatingcomprising solids derived from the organic film-forming resin, said wetuncured coating being sufficiently adherent to the metal surface toremain in place when removed from contact with the autodepositingcomposition and rinsed with water; (B) removing the metal surfacebearing the wet uncured coating formed in step (A) from contact with theautodepositing composition, and then contacting the wet uncured coatingbefore it dries or is dried with an aqueous treatment solution that hasan adjusted pH from 7 to 11 wherein prior to the adjustment of the pHsaid solution consists essentially of water and at least one componentselected from the group consisting of the following inorganic acids andsalts thereof, molybdic acid, tungstic acid, polyphosphoric acid, andpolysilicic acid wherein the total concentration of materials selectedfrom the group of molybdic acid, tungstic acid, polyphosphoric acid andpolysilicic acid and the salts of these acids is from 0.1 to 50 g/L; (C)removing the metal surface bearing the wet uncured coating, aftercontacting it with the aqueous treatment solution, from contact with anyaqueous liquid phase except for that which may be absorbed in thecoating itself; and (D) drying the wet uncured coating from the end ofstep (C) to convert the wet uncured coating into a dry solid coating. 2.A process according to claim 1, wherein the time of contact in step (B)is from 0.08 to 10 min, and step (D) includes exposing the coating to atemperature of at least 70° C. for a time of at least 2 min.
 3. Aprocess according to claim 2, wherein the time of contact in step (B) isfrom 0.5 to 1.5 min, and step (D) includes exposing the coating to atemperature of at least 90° C. for a time of at least 5 min.
 4. Acomposition according to claim 3, wherein, in the aqueous treatmentsolution used in step (B), the pH is from 7.2 to 9.8 and the totalconcentration of materials selected from the group consisting ofmolybdic acid, tungstic acid, polyphosphoric acid, polysilicic acid andthe salts of all these acids is from 0.1 to 20 g/L.
 5. A processaccording to claim 4, wherein the aqueous treatment solution with anadjusted pH of from 7.2 to 9.8 used in step (B) contains ammoniumhydroxide, ammonium bicarbonate, or both.
 6. A process according toclaim 2, wherein, in the aqueous treatment solution used in step (B),the pH is from 7.2 to 9.8 and the total concentration of materialsselected from the group consisting of molybdic acid, tungstic acid,polyphosphoric acid, polysilicic acid and the salts of all these acidsis from 0.1 to 20 g/L.
 7. A process according to claim 6, wherein theaqueous treatment solution with an adjusted pH of from 7.2 to 9.8 usedin step (B) contains ammonium hydroxide, ammonium bicarbonate, or both.8. A process according to claim 1, wherein, in the aqueous treatmentsolution used in step (B), the pH is from 7.:2 to 9.8 and the totalconcentration of materials selected from the group consisting ofmolybdic acid, tungstic acid, polyphosphoric acid, polysilicic acid andthe salts of all these acids is from 0.1 to 20 g/L.
 9. A processaccording to claim 8, wherein the aqueous treatment solution with anadjusted pH of from 7.2 to 9.8 used in step (B) contains ammoniumhydroxide, ammonium bicarbonate, or both.